abstract

Impingement jets are known to be efficient mechanisms for the exchange of heat between fluid and structure. They are generally used in industry for cooling, heating or drying. Several experimental and numerical studies have been realized to study convective heat transfers and/or to correlate the convective heat transfers to the wall with the unsteady flow of the jet (O’Donovan et al. [9] [10]). But these studies have been performed at low Mach number whereas higher Mach number are found in industrial applications as fan cooling processes for instance (M = 0.5 to 0.8). So, we propose to study the influence of Mach number of the impingement flow, ranging from 0.1 to 0.8, on convective heat exchange between a circular jet and a round axisymmetric plate. The aerodynamic of the fluid and the heat transfers depend on the following parameters: the D hydraulic diameter of the jet, the H distance to the wall, the Re Reynolds number of the flow, the M Mach number and the Tj temperature of the jet. The local convective heat transfer coefficients are experimentally determined by an inverse method based on a measurement of steady state temperature fields by infrared thermography (Fénot et al. [2]) for 1 ≤ H/D ≤ 5 and 0.1 ≤ M ≤ 0.8 . An experimental study of radial velocity fluctuations of the fluid in nearby wall has also been realized from hot wire anemometry. A spatial and temporal turbulent study (turbulence spectrum, integral turbulent scales, dissipation rate) allows to correlate convective heat transfer to the wall to aerodynamic phenomena.

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